Albite

Mineral Name: Albite

Chemical Composition: NaAlSi3O8

Color: White, colorless, cream, light yellow, light blue, light green, pale red, light brown, gray

Streak: White

Hardness: 6-6.5

Cleavage/Fracture: The cleavage is 2 at 90 degrees. This means that the cut of the rock almost makes a shape that looks like a staircase.

Crystal Form: Cubic, rectangular, triclinic which are all crystal systems with 3 axes of unequal length (1). Crystals are flat, and can occur as tall, prismatic (prism-like) or small tabular (flat, table-like) crystals (2). The crystals can exhibit twinning, such as when two crystals grow together in a symmetrical way. Crystals can also be striated, showing rows of linear lines, almost like scratches, on the cleavage planes (2).

Luster: Vitreous to pearly (6)

Special Features: Albite has common polysynthetic twinning that creates fine parallel grooves discussed above in the crystal form section (6). Also, Albite takes a longer time for crystallization than other feldspars. This allows it to form in large, well crystallized formations. This means that the samples had more time and space to form. It is also a common accessory mineral.

Varieties: Analbite, Cleavelandite, Pericline, Peristerite (2)

Mineral Group: Albite belongs to the Plagioclase Feldspar group, which is a grouping of minerals containing sodium or calcium and are also feldspars (albite contains sodium).The Plagioclase group of feldspars are a grouping of minerals that have essentially the same formula, but contain differing percentages of sodium and/or calcium. Albite is an end member of the series, containing the most sodium, while Anorthite is at the other end and contains mostly calcium (2). Albite is a part of the silicates because Albite contains silica, and the tectosilicates because it has crystalline lattice has all four oxygen atoms from each silica tetrahedron sharing itself with an adjacent silica tetrahedron. (2)

Environment: Albite forms from magma or lava in intrusive or extrusive igneous rocks, respectively. Albite is the last of the plagioclase feldspars to crystallize. It can also forms in hydrothermal veins (near volcanoes).

Common mineral associations: Hornblende, Biotite, Muscovite.

Associated Rock types: Albite is common in granites, granodiorites, rhyolite and syenite. In metamorphic rocks it is common in pelitic rocks, a fine-grained sedimentary rock that has been metamorphosed. An example of a pelite is mudstone. (9)

Occurrence in North America: Ramona, California; Haddam/Middletown, Middlesex, New York; Alaska in the Pala; Mesa Grande in San Diego, California (2,4).

Economic Uses: The economic uses of Albite is that it is used as a gemstone, due to its highly colored and sometimes iridescent qualities (2). Moonstone is a highly desirable combination of albite and orthoclase which give it colorful sheen inside the mineral. It is a common collector gem, since albite has a hardness of 6-6.5, and it is usually too fragile for jewelry, so they must be sanded down or rounded first to be made into a gemstone.

Industrial Uses: Albite is used in the manufacturing of ceramics. It is ground up and mixed together with other materials and when it is melted it acts as a cement and sticks the materials together. Sometimes Albite is also used to supply the alumina in the making of glass (3).

Scholarly Uses: Albite is important in geology as it helps geologist determine the temperature of formation, since albite forms in low heat, and helps differentiate the different types of rocks they examine, as albite is common in regional and contact metamorphic rocks. It is also used in petrography to understand the evolution of a magma as seen in zoned examples of plagioclase under microscope (2).

Notable Identification: Named in 1815 by Johan Gottlieb Gahn and Jöns Jacob Berzelius from the Latin "albus", meaning white, alluding to its usual color. (1)

How We Identified It: It can be hard to identify this mineral against other similar minerals. However, the example we have is more “cloudy” than quartz and calcite, for example, and is softer than quartz, yet harder than calcite. An easy way to identify Albite is by its polysynthetic twinning, or stripes on the cleavage plane.

Don’t Confuse It With: It could possibly be confused with Halite, to tell the difference you can lick it seeing that, unlike Halite, it is not salty. It also can have striations which potassium feldspars do not (2). It might also be confused with quartz, which has a higher hardness, or calcite, which has a much lower hardness. Spodumene can also look like albite, but has a splintery fracture (2).